Galactosidases are enzymes (

glycoside hydrolases Glycoside hydrolases (also called glycosidases or glycosyl hydrolases) catalyze the hydrolysis of glycosidic bonds in complex sugars. They are extremely common enzymes with roles in nature including degradation of biomass such as cellulose (cel ...

) that

catalyze Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

the

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

galactosides A galactoside is a glycoside containing galactose. The H of the OH group on carbon-1 of galactose is replaced by an organic moiety. Depending on whether the glycosidic bond lies "above" or "below" the plane of the galactose molecule, galactosides ...

into

monosaccharide Monosaccharides (from Greek ''monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built. They are usually colorless, water-solub ...

s. Galactosides can be classified as either alpha or beta. If the galactoside is classified as an alpha-galactoside, the enzyme is called

alpha-galactosidase α-Galactosidase ( EC 3.2.1.22, α-GAL, α-GAL A; systematic name α-D-galactoside galactohydrolase) is a glycoside hydrolase enzyme that catalyses the following reaction: : Hydrolysis of terminal, non-reducing α-D-galactose residues in α-D ...

, and is responsible for catalyzing the hydrolysis of substrates that contain α-galactosidic residues, such as

glycosphingolipid Glycosphingolipids are a subtype of glycolipids containing the amino alcohol sphingosine. They may be considered as sphingolipids with an attached carbohydrate. Glycosphingolipids are a group of lipids (more specifically, sphingolipids) and are a ...

s or

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...

s. On the other hand, if it is a beta-galactoside, it is called

beta-galactosidase β-Galactosidase (EC 3.2.1.23, lactase, beta-gal or β-gal; systematic name β-D-galactoside galactohydrolase), is a glycoside hydrolase enzyme that catalyzes hydrolysis of terminal non-reducing β-D-galactose residues in β-D-galactosides. β- ...

, and is responsible for breaking down the disaccharide lactose into its monosaccharide components,

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

and

galactose Galactose (, '' galacto-'' + ''-ose'', "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epimer of glucose. A galactose molecu ...

Both varieties of galactosidase are categorized under the EC number 3.2.1. Two recombinant forms of alpha-galactosidase are called agalsidase alfa (

INN Inns are generally establishments or buildings where travelers can seek lodging, and usually, food and drink. Inns are typically located in the country or along a highway; before the advent of motorized transportation they also provided accommo ...

) and agalsidase beta (

). Lack of alpha-galactosidase activity in leukocytes has been linked to

Fabry Disease Fabry disease, also known as Anderson–Fabry disease, is a rare genetic disease that can affect many parts of the body, including the kidneys, heart, and skin. Fabry disease is one of a group of conditions known as lysosomal storage diseases. T ...

. Galactosidases have a variety of uses, including the production of

prebiotics Prebiotics are compounds in food that induce the growth or activity of beneficial microorganisms such as bacteria and fungi. The most common example is in the gastrointestinal tract, where prebiotics can alter the composition of organisms in the ...

, the biosynthesis of transgalactosylated products, and the removal of lactose. B-galactosidase forms the basis of lac z operon in bacteria which can be used to control gene expression.

Uses

B-galactosidase can be used to track the efficiency of bacterial transformation with a recombinant plasmid in a process called Blue/White Color Screening. B-galactosidase is made up of 4 identical polypeptide chains, i.e. it has 4 identical subunits. When B-galactosidase is separated into 2 fragments, it has the unique property of regaining enzymatic activity upon the rejoining of the inactive fragments. In the process called alpha-complementation, one of the fragments (omega) is encoded by a part of a gene of the lac operon that is found in the chromosome of the bacteria, while the other fragment (alpha) is encoded by the other part of the gene that is found in the plasmid. it is only when both parts of the gene are being expressed that both the omega and alpha fragments are produced. When both fragments are present they would come together to restore the activity of B-galactosidase. However, by placing the target gene within the locus responsible for encoding the alpha fragment, one can track the presence of the desired gene in the plasmid. When the target gene is present, the alpha-fragment gene would be inactive and the alpha fragment won't be produced. In that case B-galactosidase will not be active. When the target gene is not found in the vector, the alpha fragment gene would be active, producing the alpha fragment and allowing for B-galactosidase to gain its activity. To trace the activity of B-galactosidase a colorless analog of lactose is used, X-gal. The hydrolysis of X-gal by B-galactosidase produces galactose, a blue colored compound. Therefore, when the bacteria is transformed with the recombinant plasmid B-galactosidase is inactive and the colonies appear white, but when bacteria are transformed with the original plasmid, lacking the target gene, B-galactosidase is active and the colonies appear blue.

References

External links

* {{Sphingolipid metabolism enzymes Galactosides